This invention concerns a fabric support element for use in a papermaking machine, and in particular a support mechanism for adjustably supporting a dewatering blade in a papermaking machine, or a forming section thereof.
In the manufacture of paper and board products, a highly aqueous stock consisting of about 98-99.8% water and from 0.2-2% papermaking fibers and other solids is ejected at high speed from a headbox slice onto a moving forming fabric. Adjacent the head box slice, the forming fabric passes in sliding contact over a plurality of static fabric support elements known as blades which serve to support the forming fabric, and to define a reference surface over which the forming fabric moves. Depending on the surface profile chosen for the fabric support elements, they may act as a doctoring device and assist in draining water from and generating turbulence in the stock on the forming fabric. The fabric support surfaces usually include a lead blade located more or less underneath the point at which the stock jet impinges the forming fabric, followed downstream by at least two additional blades, each of which may be flat, or profiled to act as foils (e.g. as disclosed by Wrist in U.S. Pat. No. 2,928,465) or as agitators (e.g. as disclosed by Johnson, in U.S. Pat. No. 3,874,998), although stock agitation is not typically initiated at this very early point in a forming section. The fabric contact elements, which are typically ceramic, are normally mounted onto a vertically adjustable supporting structure using either a dovetail or a T-bar support
U.S. Pat. No. 6,780,286 to Van Essen et al. discloses an apparatus by which a paper maker can alter the number of fabric support elements in contact with the forming fabric in the area immediately after the stock impinges onto the forming fabric adjacent to the head box slice so as either to enhance, to maintain, or to diminish stock activity and thereby optimize agitation in accordance with papermaking conditions to provide a product of acceptable quality. Here, a contact element with a given profile can be vertically adjusted to be out of contact with the forming fabric and a support element with a different profile vertically adjusted to be in contact with the forming fabric.
A number patents show vertically adjustable support element mounting devices for use in papermaking machines. Typical structures are shown by: Bartelmuss et al in U.S. Pat. No. 5,660,689; Bubik et al. in U.S. Pat. No. 5,262,010 and U.S. Pat. No. 5,061,347; and Jaakkola U.S. Pat. No. 5,387,320.
FIGS. 1A-1C of the present application show some of the current designs for vertically adjustable support element mounting devices on the market. FIG. 1A shows a prior art blade support device 10a having a pneumatic air tube 12 located on a support member 20. The pneumatic air tube 12 contacts the bottom of a blade support 18 upon which the blade or doctoring element 16 is mounted. Slide control surfaces 14 are provided on the support member 20 to linearly guide the blade support 18 as it is extended upwardly by inflating the pneumatic air tube 12. FIG. 1B shows a similar arrangement of a prior art blade support device 10b in which the blade support 18 moves linearly upwardly along slide control surfaces 14. FIG. 1C shows a third blade support device 10c in which the blade support 18 is constrained for linear movement via slide control surfaces 14 on the support member 20 in order to move the doctoring element or blade 16 on the blade support 18 into or out of contact with a fabric surface. In this arrangement, two separate pneumatic air tubes 12a, 12b are provided with the first pneumatic air tube 12a being inflated in order to raise the blade and the second pneumatic air tube 12b being inflated in order to retract the blade from contact with the fabric.
These prior art arrangements rely on various methods of pneumatic retraction by a second actuator (tube 12b) or no positive retraction at all. All of these prior art devices also provide a linear movement using a linear guide mechanism wherein the support structure of the doctoring blade is constrained by a static bearing surface.
The current designs on the market rely on mating surfaces, which slide to control the movement of the doctoring element. This method inherently has excessive friction, which can increase if paper fibers from the slurry enter into these arrangements resulting in less controllability and loading sensitivity. Further, a complex system is required to provide for positive extension and retraction of the doctoring blade.